Disposable absorbent articles such as disposable diapers and feminine hygiene articles are well known in the art. Such articles are designed to absorb exudates from the wearer's body. Disposable absorbent articles typically have a fluid permeable body contacting layer called a topsheet, a fluid impermeable layer called a backsheet joined to the topsheet, and an absorbent layer referred to as an absorbent core sandwiched between the topsheet and backsheet. In operation fluid exiting the wearer's body enters the disposable absorbent article through the topsheet and is stored in the absorbent core. The backsheet prevents any excess fluid that is not absorbed from exiting the disposable absorbent article. For disposable absorbent articles like sanitary napkins intended to be worn with other clothing, the backsheet can be a garment-facing layer, and typically aids in preventing soiling of the clothing.
Other elements can be included in disposable absorbent articles, including additional absorbent layers having structures designed for certain functions. For example, a secondary topsheet can be an absorbent layer placed between the topsheet and the absorbent core, and having a structure designed to wick fluid quickly away from the topsheet and into the absorbent core. Likewise, multiple layers of absorbent cores can be used, each layer having fluid handling properties designed to securely move fluid into the absorbent core for secure storage. Additionally, each layer of absorbent core material can itself be a layered or laminate structure having discrete layers as is known in the art of air laying webs using multiple air laying heads or beams. In a layered absorbent core material, any one discrete layer can comprise a different type or blend of fibers with respect to one other discrete layer.
It is known to design absorbent cores having a structure such that fluid movement from the topsheet toward the backsheet, i.e., away from the wearer's body, is facilitated. For example, fibrous layered absorbent cores in which the capillarity of the fibrous layers is increased with each layer are known. Likewise, it is known to have layered absorbent cores wherein with each succeeding layer in a direction away from the topsheet the permeability is decreased. In this manner, fluid entering through the topsheet first encounters a layer having high permeability and low capillarity to facilitate quick fluid uptake. From this first layer, the fluid can encounter a layer having less permeability and higher capillarity, such that the fluid continues to move away from the topsheet, but at a slower rate. This is generally acceptable because once the fluid is away from the wearer's body the rate at which it moves to other portions of the absorbent core is not critical.
In known absorbent cores there is a well-known tradeoff between the permeability of a material and its capillarity. In general, known materials that are relatively higher in permeability are relatively lower in capillarity, and vice versa. For disposable absorbent articles, in which it is desirable to have both parameters uncoupled, a positive change in one of these parameters results in a corresponding negative change in the other. Because permeability directly affects a material's acquisition rate and capillarity directly impacts the movement of fluid due to limits in capillary pressure, this tradeoff in properties has, in the past, resulted in an absorbent core chosen for a balance of properties. The necessary tradeoff, however, has resulted in absorbent structures, including absorbent cores, in which the desired levels of acquisition rate and effective fluid movement to secure storage cannot be achieved simultaneously.
Accordingly, it would be desirable to have an absorbent article and an absorbent core material in which both permeability and capillarity pressure can be maintained at desirable levels simultaneously in an absorbent core.
Additionally, it would be desirable to have an absorbent article and an absorbent core material in which the negative aspects of either of permeability or capillarity pressure when one or the other is more optimized, are minimized.
Further, it would be desirable to have an absorbent article and an absorbent material in which the tradeoff between permeability and capillarity pressure is managed such that delivering relatively higher permeability can be accomplished without a decrease in capillarity pressure.